by Trevor Woods |Last Updated: March 10, 2020
You expect your plumbing to be rather silent. The quiet whoosh of water through your home’s pipes flows gently, then BANG! The sudden closing of a water valve sends hydraulic shock waves reverberating through your waterlines. The once fast-moving water has nowhere to go after the outlet is closed, resulting in an intense surge in pressure causing your pipes to jerk and slam against nearby walls and framing.
The pounding sound of hundreds of pounds per inch of pressure is more than alarming, it’s a warning sound of excessive wear on pipes and impending leaks. Left unchecked, water hammer can be so forceful that it breaks pipes, damages plumbing joints, harms faucets and appliances, or loosen water line fasteners.
This plumbing peril is not solely experienced by households with copper or metallic water lines. Plastic piping materials like PEX, Poly B, or CPVC are also subject to water hammer although you won’t hear it as loudly. Luckily the remedy for water hammer is simple and most homeowners can easily fix it without calling a professional for help.
We will explain in depth what water hammer is, what causes it, the effects it has on your plumbing, and how to fix it!
What Is Water Hammer?
Water hammer is nothing new. It has been described as far back as the 1st Century B.C. in Roman stone tubes and lead pipes. But the installation of modern water distribution systems, fixtures, and appliances water hammer has become an increasing cause for concern.
The condition commonly known as water hammer is technically a form of hydraulic shock. A surge in fluid pressure when the momentum of a liquid in motion changes direction or is forcefully stopped. The banging you hear is the reflected energy’s shockwave transmitted through the fluid and into the piping system causing your water pipes to strike wooden framing or drywall. It sounds like someone is inside your home using a hammer to pound nails, which is where the name comes from.
What Causes Water Hammer?
There are several causes of water hammer; appliances and fixtures with fast-closing valves, flooded air chambers, excessive water pressure, valve and water pump failures, and loose water lines. Fast closing valves and flooded air chambers are the most common culprits so we will cover them first.
Fast Closing Valves
This situation commonly occurs when household fixtures or appliance valves close suddenly. Typically taking place at clothes washers and dishwashers that have solenoid valves that can stop the flow of water quickly thereby building up high-pressure shockwaves that reverberate through your piping. Toilets, faucets, and other shower fixtures can also be subject to water hammer but much less frequently.
Flooded Air Chambers
Another cause of water hammer is the flooding of air chambers in your piping system. Air chambers are often designed into your water piping system. They are vertical sections of pipe that are filled with air to help regulate pressure and preventing hydraulic shockwaves from forming. Because air is more compressible than water, they act as shock absorbers with the trapped air cushioning the momentum of the water in the pipes.
Excessive Water Pressure
The average household water pressure varies depending on where you live but typically it should not exceed 80 psi. Water pressure above this level increases the chances of harming your plumbing fixtures and magnifies the possibility of water hammer and worsens it’s effects.
Not sure if your water pressure is too high? Try this water pressure gauge to test your home:
Water Pump Or Valve Failure
A less common but just as serious cause of water hammer is sudden pump shutdown. If your plumbing system has a booster pump to help with increasing water pressure or a pump on your hot water system you may be subject to significant hydraulic shock if these pumps fail or seize.
Valve failure can occur anywhere in your plumbing system but is more likely associated with check valves. These valves are prone to slamming shut rapidly because they rely on reversing the flow of water and creating back-pressure to operate. You can find these types of valves on irrigation or sprinkler services, boilers and hydronic heating systems, and recirculation lines to name a few locations. When these valves start to fail you will notice a chattering, repetitive banging, or even shuddering as the shockwave travels back and forth in the plumbing system.
Loose pipes don’t necessarily cause water hammer but they do amplify it’s effects. Free-floating or unsecured waterlines that have come loose from water hammer will increasingly rattle and slap against joists, wooden framing, HVAC ductwork, other plumbing pipes, or drywall. What a racket!
What Are The Effects Of Water Hammer?
Water hammer is more than just an alarming sound. The resulting pressure spike from hydraulic shock can reach 5 to 10 times the normal operating pressure of your plumbing system. Repeated exposure to water hammer can be a destructive force; loosening pipe fasteners, and damaging your pipe walls, joints, pressure gauges and sensors, flow meters, and fixtures. In extreme cases, it can create a vacuum in the pipe downstream from the valve that may cause the pipe to collapse or implode.
Cracked pipes, leaking joints, and damage to appliances can add up to costly repairs if water hammer is left unchecked. And in some situations, the extreme pressure of a burst pipe could be a significant safety hazard to anyone in the vicinity of a pipe when it ruptures. The consequences of water hammer pose serious harm to you and your home.
How To Fix Water Hammer
Depending on where you are experiencing water hammer will dictate how you go about stopping it. We will cover the best practices for mitigating hydraulic shock in each plumbing situation with simple and easy to follow steps.
Fast Closing Valves
Sudden valve closure is most often associated with quarter-turn or automated solenoid valves. Sometimes a single appliance like a dishwasher or laundry machine is responsible for pressure spikes as the appliance controls the flow of water during cleaning cycles. To find the culprit appliance, pay close attention to when your water hammer occurs. If hydraulic shock is noticed only when that machine runs, you’ve found the cause to your pipe-pounding.
You may choose a process of elimination, narrowing your search one fixture at a time, but when you do locate the cause of the water hammer you can install a water hammer arrestor. These hammer arrestors, also called water surge arrestors, are air-filled chambers that operate like shock absorbers that buffer the jolt in water pressure when an appliance slams a water valve shut.
These water hammer arrestors provide point of relief for pressure spikes and reduce noise and stress on the piping system. They are also the ideal solution to solve water hammer where installing air chambers is impractical or not permitted due to local plumbing codes. Mechanical water arrestors are low maintenance and do not need to be recharged like air chambers. But they do need to replaced when the inner springs or bladders wear out.
Water hammer arrestors are widely available and are selected for the appliance they serve and the location of the installation. A washing machine, for instance, will require you to install hammer arrestors on both Hot and Cold water supply lines.
Dishwashers utilize smaller surge arrestors that thread onto existing shutoffs and supply lines.
Inline style arrestors can be installed on a single water line if space and location permits. These can be added to any standard sized waterline to alleviate water hammer.
Keep water hammer prevention in mind whenever you are renovating or doing new plumbing installations. Water hammer arrestors can be integrated into service boxes and supply valves for most appliances and applications.
Installing Water Hammer Arrestors
Installing water hammer arrestors is a great solution to eliminating hydraulic shock caused by fixtures or appliances and is easy to complete in a few minutes with just some basic hand tools.
Tools And Materials Needed
- Bucket or small container to catch water
- Towel or shop rags
- Adjustable Wrench or Slip Joint Pliers
- Plumber’s Tape
- Hammer Arrestors appropriate for your application
1. Turn Off The Water
Start off by isolating the appliance or fixture location in which you wish to install the hammer arrestor. Most shutoffs will be located close to the plumbing fixture they serve. Turn the valve handle clockwise to shut the water OFF.
If you cannot find the individual shutoff you may need to turn the main water supply to your home OFF.
If you are installing water hammer arrestors on a clothes washer or laundry machine, be sure to turn off both Hot and Cold water supplies.
2. Disconnect The Supply Lines
With a wrench or channellock pliers disconnect the
Watch Your Distance
Hammer arrestors should be installed within six feet of the culprit valve.
Some applications will require the use of plumber’s tape on the male or exposed threads of the new connections. Wrap all the male threaded connections with two or three layers of
4. Install The Water Hammer Arrestor
Thread the surge arrestor onto each valve or inlet pipe. Turn the connection clockwise until hand-tight.
Any Direction Works
Hammer arrestors can be installed at any angle so don’t worry if you are unable to orient the arrestor vertically.
Finish tightening the connection with a wrench or pliers until snug and water-tight. Repeat if you are doing hot and cold water supplies to the same fixture.
5. Reconnect Water Supply Lines
Reconnect the supply tubes or hoses and tighten the connections with with your trusty wrench or pliers.
6. Turn On Water And Test Your Connections
Now you can turn the water valves back on to check for water leaks. Slowly open the water valves counterclockwise until the valve is completely open. Look for any dribbles or drips on the threaded connections you have made. Tighten any joints as necessary.
Complete your testing by turning on the fixture or running the appliance through a wash cycle. Inspect for any leaks again and make any final adjustments as needed. Listen carefully for any pounding, banging, rattling, or other signs of water hammer.
All quiet? Great! Soak up any water that may have dribbled out during installation or testing and you’re done!
Flooded Air Chambers
Air chambers are often found in older homes and are fabricated during the installation of the plumbing system. They are built on-site by the plumber and are often installed on hot and cold waterlines before they reach a plumbing fixture or appliance. Be aware that some areas have building codes that rule out the installation of new air chambers in favour of newer mechanical hammer arrestors.
These air chambers are comprised of ordinary plumbing fittings and made with a tee-fitting that is installed on a water line that extends a vertical section of capped pipe. This dead-end section of plumbing traps a pocket of air outside the area of normal water flow to act as a cushion when water valves are closed. Air chambers will help alleviate hydraulic shock when water is stopped or changes direction suddenly and effectively cures water hammer.
In many houses, air chambers are installed inside the walls at critical spots throughout your home. Some building codes prescribe that air chambers be installed alongside common sources of water hammer like washing machines and shower valves. Because air chambers are often in concealed locations they are rarely visible unless the plumbing is exposed in mechanical or utility areas, unfinished rooms, or crawlspaces.
The problem with these constructed air chambers is that they can fill up with water over time. A waterlogged air chamber will not function properly and the symptoms of water hammer will return. The good news is that air chambers can be easily recharged by draining your waterlines and allowing air to flow into the chambers and restoring their shock-absorbing ability.
If you find that you don’t have air chambers in your home, please see our above section on how to install mechanical hammer arrestors yourself.
1. Shut Off The Main Water Valve
Find the wain water line that serves your home and turn the valve off completely. If you have a hand-wheel style valve, twist the handle clockwise until the valve is closed. A lever or quarter-turn valve handle must be turned clockwise until the handle is perpendicular to the pipe.
2. Open The Highest Water Valve
Turn on the highest faucet or shower valve in your home. If you are not sure which fixture to choose, you can also open all the faucets to help the water drain quickly.
Purge Your Pipes
Make sure you drain both hot and cold water supplies by opening Hot and Cold handles or single-handle fixtures to a middle position.
3. Open The Lowest Water Valve
Drain all the water from your pipes by opening the lowest faucet in your home. This may be a lawn service, basement sink, or a draincock located on your water main shutoff valve.
As the suspended water in your pipes drains out air will automatically flow into the plumbing system and refill the air chambers. Once the water has stopped flowing from the lowest fixture or valve it can be turned OFF.
4. Open The Main Water Valve
Now you can turn the water back on to your plumbing system. Water will flow through your water lines and push out any excess air left in the pipes. Once your uppermost faucet or valve has finished coughing, sneezing, and expelling any remaining air you can turn the plumbing fixtures OFF.
Done! You have now successfully recharged your air chambers and prevented the damages caused water hammer.
Periodically drain your plumbing to prevent the flooding of your air chambers. You can conveniently schedule this maintenance when you winterize your hose bibs or lawn services./p>
On very rare occasions your air chamber can become clogged with mineral deposits or debris. This may require you to repeat steps 1 through 4 several times to refill the air chambers. If the air chambers are accessible, the caps may need to be removed to have the pipes cleaned and scoured properly. Air chambers that are one pipe size larger than the water lines they are installed on can help prevent clogging.
If you have effectively restored your air chambers and you are still experiencing water hammer you may be suffering from high water pressure.
Excessive Water Pressure
High water pressure can cause and worsen hydraulic shock. If you have above-average water pressure you will also hear water hammer more frequently and throughout your whole home as opposed to at a single faucet or appliance.
Start by checking your water pressure to verify if it’s higher than normal. Many cities and municipalities will inspect your water pressure for free and offer to reduce the pressure if necessary.
Water Pressure Testing
Testing water pressure can easily be done yourself with the aid of a gauge and
1. Turn Off The Water
When you have your test gauge ready, start by turning OFF all the fixtures and appliances that use water. You don’t want a dishwasher or faucet running during the test because it will obscure the results.
2. Install The Test Gauge
Close the water valve at your testing location. Disconnect any supply lines or tubes if necessary. With the appropriate adaptor, screw the pressure gauge onto a valve or supply line at the fixture you are checking.
Measure At The Meter
Choose a valve or
3. Test Your Water Pressure
Turn ON the valve that the pressure gauge is attached to slowly until it’s fully open and the needle on the gauge stops moving. Remember or record this number and repeat this test a few times to ensure the gauge measures the same pressure each time.
If your pressure reading exceeds 80 psi you need to adjust your home’s pressure regulator or have one installed. Normal water pressure can run anywhere between 30 to 55 psi. But pressure exceeding 100 psi can damage your plumbing fixtures, faucets, and appliances.
4. Remove The Pressure Gauge
Turn the water valve OFF at your testing location to isolate the test gauge. Be prepared that when you unthread the test gauge connection some water will dribble out. Have a small container or
Reconnect the supply lines you disconnected earlier and test them for leaks. Retighten as necessary. Done!
If you already have a pressure reducing valve (PRV) installed in your home, adjust the pressure to an appropriate operating range. Most PRVs are located on your home’s main water supply. Depending on the manufacturer, some pressure reducing valves have a handle, screwdriver slot, or a wrench location to make adjustments. Recheck your water pressure each time you change your pressure reducing valve’s settings.
Slow And Steady
Take your time and make several small incremental pressure changes, checking your pressure gauge with each adjustment.
We recommend setting your water pressure to 50 psi. This pressure is adequate for most homes to function normally and avoid water hammer with the additional benefit of promoting water conservation. Your fixtures and appliances will also appreciate the reduced pressure and potentially prolonging their life spans.
If your home is not equipped with a pressure reducing valve, one should be installed on your main water supply so that it can effectively protect your whole home from high water pressure. With a PRV positioned where the main water line enters the building you will be shielded from water hammer resulting from excessive water pressure.
If you consider yourself a serious DIYer you can tackle this project but if you are uncomfortable with potentially cutting into your plumbing system we recommend contacting a local professional to install a pressure reducing valve for you. We have a resource on choosing the right plumber for you that you can read HERE.
Water Pump or Valve Failure
Pump failure and shutdown are less common in households but remain a significant cause of water hammer. Water pressure boosters, recirculation systems, and boilers are all subject to pump failure. Water hammer caused by deteriorating pump performance is experienced prior to the pump seizing completely.
This cause of hydraulic shock is easily remedied by repairing or replacing the damaged pump.
You can also help alleviate water hammer from pump shut down by installing pumps with internal check valves. These valves can be extremely effective in reducing and sometimes eliminating water hammer conditions.
Additionally, water hammer resulting from sudden pump shutdown can be minimized by installing silent check valves as close to the pump as possible or with check valves on vertical sections of water line piping.
Valves can also have a role in causing hydraulic shock. This can result from improper valve selection, location of installation, or poor valve maintenance practices. Certain valves like swing check and double-check valves can contribute to water hammer problems and should be exchanged with silent on non-slam check valves.
Silent or non-slam check valves do not rely on gravity or fluid flow for their closure. Rather they close upon the decrease in a pressure differential across the valve body and thus are far less likely to slam shut and induce water hammer.
Pump and valve selection can be a very technical subject matter and are typically best left to designers, plumbers, and engineers to know what types of pumps and valves are appropriate to utilize in each installation and application.
Even mild water hammer shock waves can be exaggerated by poorly secured water lines, allowing loud banging against your home’s structural features. During your home’s construction plumbers fastened the water-supply lines to studs and joists using clips and strapping to support the weight of the pipes and the water held inside. Older water supply pipes are often insufficiently secured and pipes that have been subject to water hammer can loosen there supports over time.
You can prevent amplified noise from water hammer by tightening any loose straps or hangers and adding a few more if some are missing to improve stability.
1. Check For Loose Waterlines
Head to your basement, crawlspace, mechanical room, or any area with visible waterlines. Bring a
If you can’t locate any loose pipes it may help to have another person run some water through each fixture while you locate the source of water hammer noise.
2. Support The Waterlines
After you have found some pipes in need of some reinforcements, you need to tighten existing pipe straps with a screwdriver or add a few new supports. You will need some pipe clips, clamps, hangers, or plumbers strapping to secure the pipes more soundly.
Most pipe supports are made from metal or plastic but you can also find padded pipe clips for additional vibration reduction. Secure all the accessible pipes as best you can.
Don’t Risk Rusting
Avoid galvanic corrosion by choosing the right pipe supports. Make sure you do not use dissimilar metals when securing metal pipes. A galvanized steel support could react poorly with copper plumbing causing electrolysis and corroded pipes. This corrosion could result in the deterioration of the pipe support and plumbing leaks. Try to use similar metal clamps or plastic clips to prevent pipe damage.
The addition of pipe insulation can help cushion loose or banging pipes. Pipe insulation is available in foam tubes that are slit and designed to slip over water lines. Originally designed to prevent pipes from freezing, pipe insulation can also serve as cushions to prevent pipes from thumping against studs or joists.
Insulating pipes is easiest in mechanical areas or wherever plumbing lines are exposed and accessible. Not only will this help silence noisy pipes but it will also increase energy efficiency by insulating waterlines and preventing heat loss.
Water hammer may not seem like anything more than a nuisance noise but the consequences can be quite costly. Fortunately, you can fix water hammer in your home without breaking the bank. For pre-existing household plumbing, installing water hammer arrestors can eliminate the damaging effects of hydraulic shock. Your plumbing and your wallet will thank you!
Trevor Woods is the founder of Plumb University® and he started in the plumbing and construction industry in 1997. Since then, his mission is to make plumbing repair and maintenance easy for everyone. And each year, he continues to help more people with their plumbing installation, care, and troubleshooting.